Fiberoptic gyroscopes are well known in the art and are generally an attractive means for sensing rotation, as they can be made quite small and still be constructed to withstand considerable mechanical shock, temperature change, and other environmental extremes. While there are various forms of optical sensors which utilize the well known Sagnac effect to detect rotation about appurtenant axis of the device, typical fiberoptic gyroscopes employ a single optical fiber of substantial length which is formed into a coil by being wound on a core or bobbin to form a closed optical path. An electromagnetic wave, typically generated by a light source, is introduced and split into two light beams to propagate in opposite directions through the coil. The waves ultimately are caused to interact with a photo detector. The path length differences between the pair of electromagnetic waves during angular rotation introduces a phase shift between those waves so that the output signal depends on the length of the entire optical path through the coil traversed by the two opposing directional electromagnetic waves.
An exemplary block diagram of a typical fiberoptic gyroscope is shown in FIG. 1. As shown the fiberoptic gyroscope includes a light source 10, a detector 40, an optical fiber coil 30, a modulator 26, a coupler 14, a polarizer 22, and an integrated optics chip 20. As is known, when an electromagnetic wave is emitted from source 10, it passes through coupler 14, is appropriately polarized by polarizer 22, and thereafter split by optical splitter 24 into two beams. Each beam is conducted along two optical paths, one through optical cable 28 and one through optical cable 29. Each of the beams propagate through coil 30 (one being a clockwise beam and the other a counterclockwise beam). The rotation of coil 30 causes a phase difference between the beams, and the amount of rotation can be obtained by detecting the phase difference. Modulator 26 is utilized, as is known, to realize a desired sensitivity. Detector 40 is utilized to detect the intensity of the interference beam thus obtained, the intensity of the interference beam is converted into an error signal used to provide loop closure in the signal processing circuit mounted on board 50.
Such fiberoptic gyroscope constructions are typically formed in various sizes and configurations. Orientation of multiple fiberoptic gyroscope of the type shown in FIG. 1, such as by appropriately orienting three single axis fiberoptic gyroscopes in a suitable fashion, the size of the system becomes large, unwieldy, and complex to manufacture. Alternatives to such oversized configurations are known.
Various attempts to design and develop a compact, easy to manufacture fiberoptic gyroscope have been attempted. For example, a depolarized fiberoptic gyroscope based inertial measurement unit disclosed by the Naval Weapons Center in an article entitled "The Depolarized Fiber-Optic Gyro for Future Tactical Applications," published in SPIE Volume 1367 Fiberoptic and Laser Sensors VIII (1990), p. 155 et seq., discloses a compact three-axis fiberoptic gyroscope concept in which three fiberoptic coils pick up each of the three orthogonal axis of rotation. Associated drive electronics for proper operation of each of the three gyro axis are disclosed as likely being contained within the package (see FIG. 9).
In U.S. Pat. No. 4,717,256 issued Jan. 5, 1988, to Ensley, et al., and assigned to the U.S.A. as represented by the Secretary of the Navy, a fiberoptic rate sensor is disclosed. In accordance with one embodiment, single-axis and three-axis packages comprising compact units are shown. (See FIGS. 11 and 12.) In these embodiments, the glass fiber is wound around a metal frame to form a coil with the other elements of the sensor mounted within the frame.
Similarly, U.S. Pat. No. 5,357,339 issued Oct. 18, 1994, to Teraoka, et al., and assigned to Hitachi Cable Ltd., relates to a multi-axis fiberoptic gyroscope assembly. The '339 patent discloses individual fiberoptic gyroscope units shaped like tetragonal cones, which are mounted to a square plate used as a base to hold the light source, detector, and coil. The single-axis gyroscope unit disclosed therein occupies a unit shape comprising a tetragonal pyramid. Ostensibly, a plurality of identical one-axis gyroscope units can be combined to form a three-axis fiberoptic gyroscope.
Various multi-axis fiberoptic gyroscope assemblies in which the plural fiber coils share common electric components are also known. For example, U.S. Pat. No. 5,194,917 issued Mar. 16, 1993, to Regener and assigned to Standard Elektrik Lorenze Aktiengesellschaft, discloses a fiberoptic gyroscope integrated on a silicon substrate, U.S. Pat. No. 5,294,972 issued Mar. 15, 1994, to Kemmler and assigned to Lite GmbH discloses a multi-axis fiberoptic rotation rate sensor with parallel sensing coils, and finally, U.S. Pat. No. 5,085,501 issued Feb. 4, 1992, to Sakuma, et al., and assigned to Japan Aviation Electronics Industry Ltd., discloses a fiberoptic gyroscope using optical wave guide couplers. In the '501 patent, the optical integrated circuit substrate is fixed to a reinforcing plate, which in turn is held on a support structure by flexible holding means.
Each of these attempts, however, while providing some modicum of ease of manufacture, does not fully address the need, which is long felt, for a fiberoptic gyroscope design which is versatile and easy to manufacture. In general, while prior attempts have been made to devise and design a low cost manufacturing approach for fiberoptic gyroscopes the currently available prior art does not adequately meet this need.